Stressor-specific regulation of distinct brain-derived neurotrophic factor transcripts and cyclic AMP response element-binding protein expression in the postnatal and adult rat hippocampus

Kappa Opioid Receptor Activation Induces Epigenetic Silencing of Brain-Derived Neurotropic Factor via HDAC5 in Depression

Treatment-resistant depression (TRD) occurs in almost 50% of the depressed patients. Central kappa opioid receptor (KOR) agonism has been demonstrated to induce depression and anxiety, while KOR antagonism alleviates depression-like symptoms in rodent models and TRD in clinical studies. Previously, we have shown that sustained KOR activation leads to a TRD-like phenotype in mice, and modulation of brain-derived neurotrophic factor (BDNF) expression in the prefrontal cortex (PFC) appears to be one of the molecular determinants of the antidepressant response. In the present study, we observed that sustained KOR activation by a selective agonist, U50488, selectively reduced the levels of Bdnf transcripts II, IV, and Bdnf CDS (protein-coding Exon IX) in the PFC and cultured primary cortical neurons, which was blocked by selective KOR antagonist, norbinaltorphimine. Considering the crucial role of epigenetic pathways in BDNF expression, we further investigated the role of various epigenetic markers in KOR-induced BDNF downregulation in mice. We observed that treatment with U50488 resulted in selective and specific downregulation of acetylation at the ninth lysine residue of the histone H3 protein (H3K9ac) and upregulation of histone deacetylase 5 (HDAC5) expression in the PFC. Further, using anti-H3K9ac and anti-HDAC5 antibodies in the chromatin immune precipitation assay, we detected decreased enrichment of H3K9ac and increased HDAC5 binding at Bdnf II and IV transcripts after U50488 treatment, which were blocked by a selective KOR antagonist, norbinaltorphimine. Further mechanistic studies using HDAC5 selective inhibitor, LMK235, in primary cortical neurons and adeno-associated viral shRNA-mediated HDAC5-knockdown in the PFC of mice demonstrated an essential role of HDAC5 in KOR-mediated reduction of Bdnf expression in the PFC and in depression-like symptoms in mice. These results suggest that KOR engages multiple pathways to induce depression-like symptoms in mice and provide novel insights into the mechanisms by which activation of KOR regulates major depressive disorders.

Caffeine Administration Mitigates Chronic Stress-Induced Behavioral Deficits, Neurochemical Alterations, and Glial Disruptions in Rats

Prolonged exposure to stress has detrimental effects on health, and the consumption of caffeine, mostly contained in energy drinks, has become a widely adopted stress coping strategy. Currently, there is limited information regarding the effects of caffeine intake on chronic stress exposure. Thus, this study investigated the effects of caffeine administration on chronic stress-induced behavioral deficits, neurochemical alterations, and glial disruptions in experimental rats. Thirty male Wistar rats were randomly assigned to five groups (n = 6): non-stress control, stress control, and caffeine groups of doses 12.5, 25, and 50 mg/kg. The stress control and caffeine groups were subjected to an unpredictable chronic mild stress (UCMS) protocol daily for 14 days. The rats were evaluated for phenotypic and neurobehavioral assessments. Thereafter, the rat brains were processed for biochemical and immunohistochemical assays. Caffeine administration was found to ameliorate behavioral dysfunctions in rats exposed to UCMS. The UCMS-induced changes in brain levels of monoamines, cholinesterases, and some oxidative stress biomarkers were reversed by caffeine. Caffeine administration also produced mild protective effects against UCMS-induced changes in GFAP and Iba-1 expression in stress-specific brain regions. These results showed that low and moderate doses of caffeine reversed most of the stress-induced changes, suggesting its ameliorative potential against chronic stress-induced alterations.

Effects of Tail Pinch on BDNF and trkB Expression in the Hippocampus of Roman Low- (RLA) and High-Avoidance (RHA) Rats

In this article, we describe the effects of tail pinch (TP), a mild acute stressor, on the levels of brain-derived neurotrophic factor (BDNF) and its tyrosine kinase receptor B (trkB) proteins in the hippocampus (HC) of the outbred Roman High- (RHA) and Low-Avoidance (RLA) rats, one of the most validated genetic models for the study of fear/anxiety- and stress-related behaviors. Using Western blot (WB) and immunohistochemistry assays, we show for the first time that TP induces distinct changes in the levels of BDNF and trkB proteins in the dorsal (dHC) and ventral (vHC) HC of RHA and RLA rats. The WB assays showed that TP increases BDNF and trkB levels in the dHC of both lines but induces opposite changes in the vHC, decreasing BDNF levels in RHA rats and trkB levels in RLA rats. These results suggest that TP may enhance plastic events in the dHC and hinder them in the vHC. Immunohistochemical assays, carried out in parallel to assess the location of changes revealed by the WB, showed that, in the dHC, TP increases BDNF-like immunoreactivity (LI) in the CA2 sector of the Ammon's horn of both Roman lines and in the CA3 sector of the Ammon's horn of RLA rats while, in the dentate gyrus (DG), TP increases trkB-LI in RHA rats. In contrast, in the vHC, TP elicits only a few changes, represented by decreases of BDNF- and trkB-LI in the CA1 sector of the Ammon's horn of RHA rats. These results support the view that the genotypic/phenotypic features of the experimental subjects influence the effects of an acute stressor, even as mild as TP, on the basal BDNF/trkB signaling, leading to different changes in the dorsal and ventral subdivisions of the HC.

BDNF gene hydroxymethylation in hippocampus related to neuroinflammation-induced depression-like behaviors in mice

BACKGROUND

Neuroinflammation is a multifactorial condition related to glial cells and neurons activation, and it is implicated in CNS disorders including depression. BDNF is a crucial molecule that related to the pathology of depression, and it is the target of DNA methylation. DNA hydroxymethylation, an active demethylation process can convert 5-mC to 5-hmC by Tets catalyzation to regulate gene transcription. The regulatory function for BDNF gene in response to neuroinflammation remains poorly understood.

METHODS

Neuroinflammation and depressive-like behaviors were induced by lipopolysaccharide (LPS) administration in mice. The microglial activation and cellular 5-hmC localization in the hippocampus were confirmed by immunostaining. The transcripts of Tets and BDNF were examined by qPCR method. The global 5-hmC levels and enrichment of 5-hmC in BDNF gene in the hippocampus were analyzed using dot bolt and hMeDIP-sequencing analysis.

RESULTS

LPS administration induced a spectrum of depression-like behaviors (including behavioral despair and anhedonia) and increased expression of Iba-1, a marker for microglia activation, in hippocampus, demonstrating that LPS treatment cloud provide stable model of neuroinflammation with depressive-like behaviors as expected. Our results showed that Tet1, Tet2 and Tet3 mRNA expressions and consequent global 5-hmC levels were significantly decreased in the hippocampus of LPS group compared to saline group. We also demonstrated that 5-hmC fluorescence in the hippocampus located in excitatory neurons identified by CaMK II immunostaining. Furthermore, we demonstrated that the enrichment of 5-hmC in BDNF gene was decreased and corresponding BDNF mRNA was down-regulated in the hippocampus in LPS group compared to saline group.

CONCLUSION

Neuroinflammation-triggered aberrant BDNF gene hydroxymethylation in the hippocampus is an important epigenetic element that relates with depression-like behaviors.

Chronic haloperidol administration downregulates select BDNF transcript and protein levels in the dorsolateral prefrontal cortex of rhesus monkeys

Post-mortem studies in the prefrontal cortex and hippocampal formation from schizophrenia patients have revealed significant disruptions in the expression molecules associated with cytoarchitecture, synaptic structure, function, and plasticity, known to be regulated in part by brain derived neurotrophic factor (BDNF). Interestingly, several studies using postmortem brain tissue from individuals diagnosed with schizophrenia have revealed a significant reduction in BDNF mRNA and protein levels in the dorsolateral prefrontal cortex (DLPFC), hippocampus and related areas; however, differentiating the effects of illness from antipsychotic history has remained difficult. We hypothesized that chronic antipsychotic treatment may contribute to the altered BDNF mRNA and protein expression observed in post-mortem brains of individuals diagnosed with schizophrenia. To address the influence of antipsychotic administration on BDNF expression in the primate brain, rhesus monkeys orally administered haloperidol, clozapine, or vehicle twice daily for 180 days. We found BDNF splice variants 4 and 5 in the DLPFC and variant 2 in the EC were significantly down-regulated following chronic administration of haloperidol. In addition, proBDNF and mature BDNF expression in the DLPFC, but not the EC, were significantly reduced. Based on the known regulation of BDNF expression by BDNF-AS, we assessed the expression of this lncRNA and found expression was significantly upregulated in the DLPFC, but not EC. The results of the present study provide evidence of haloperidol-induced regulation of BDNF mRNA and protein expression in the DLFPC and suggest an important role for BDNF-AS in this regulation. Given the role of BDNF in synaptic plasticity, neuronal survival and maintenance, aberrant expression induced by haloperidol likely has significant ramifications for neuronal populations and circuits in primate cortex.

Early Life Stress Alters Expression of Glucocorticoid Stress Response Genes and Trophic Factor Transcripts in the Rodent Basal Ganglia

Early life stress shapes the developing brain and increases risk for psychotic disorders. Yet, it is not fully understood how early life stress impacts brain regions in dopaminergic pathways whose dysfunction can contribute to psychosis. Therefore, we investigated gene expression following early life stress in adult brain regions containing dopamine neuron cell bodies (substantia nigra, ventral tegmental area (VTA)) and terminals (dorsal/ventral striatum). Sprague-Dawley rats (14F, 10M) were separated from their mothers from postnatal days (PND) 2-14 for 3 h/day to induce stress, while control rats (12F, 10M) were separated for 15 min/day over the same period. In adulthood (PND98), brain regions were dissected, RNA was isolated and five glucocorticoid signalling-related and six brain-derived neurotrophic factor (Bdnf) mRNAs were assayed by qPCR in four brain regions. In the VTA, levels of glucocorticoid signalling-related transcripts differed in maternally separated rodents compared to controls, with the Fkbp5 transcript significantly lower and Ptges3 transcript significantly higher in stressed offspring. In the VTA and substantia nigra, maternally separated rodents had significantly higher Bdnf IIA and III mRNA levels than controls. By contrast, in the ventral striatum, maternally separated rodents had significantly lower expression of Bdnf I, IIA, IIC, IV and VI transcripts. Sex differences in Nr3c1, Bag1 and Fkbp5 expression in the VTA and substantia nigra were also detected. Our results suggest that early life stress has long-lasting impacts on brain regions involved in dopamine neurotransmission, changing the trophic environment and potentially altering responsiveness to subsequent stressful events in a sex-specific pattern.

Hesperidin Preserves Cognitive Functions and Hippocampus Histological Architecture in Albino Wistar Rats Subjected to Stress Through Enhancement of Brain-Derived Neurotrophic Factor

Hesperidin (HSD) is a natural compound with antioxidant potential. On the other hand, chronic stress had been linked to impaired cognitive functions as it affects many neurotransmitters and brain regions such as the hippocampus. The current study was conducted to examine the effect of HSD on learning and memory after chronic mild stress. Albino Wistar rats were subjected to chronic mild stress with HSD administered as supplements. HSD was found to decrease hippocampal amyloid beta and malondialdehyde levels, in addition, to preserve cognitive functions together with preserving hippocampus histological architecture. In conclusion, the present study sheds the light on the potential of HSD to ameliorate the deleterious effects of chronic mild stress on cognitive functions through brain-derived neurotrophic factor enhancement and reduction in Aβ formation in addition to activation of the antioxidant pathway.

Vitamin D3 administration prevents memory deficit and alteration of biochemical parameters induced by unpredictable chronic mild stress in rats

The present study aimed to investigate the effects of vitamin D3 (Vit D) administration on memory function, hippocampal level of amyloid-beta (Aβ), brain-derived neurotrophic factor (BDNF) and oxidative stress status in a rat model of unpredictable chronic mild stress (UCMS). Vit D was intraperitoneally administered at doses of 100, 1000, and 10,000 IU/kg. Animals were subjected to UCMS for a total period of 4 weeks. Memory function was assessed using morris water maze (MWM) and passive avoidance (PA) tests. Biochemical markers were measured to reveal the status of oxidative stress and antioxidant defense system. In addition, the levels of Aβ and BDNF were measured in hippocampal region. In the UCMS group, latency to find the platform was greater and the time spent in target quadrant (MWM test) as well as the latency to enter the dark compartment (PA test), were less than the vehicle group. Hippocampal malondialdehyde (MDA) and Aβ concentrations in the UCMS group were higher than the vehicle group. Hippocampal level of thiol and BDNF plus the activities of catalase and superoxide dismutase (SOD) were reduced in UCMS group compared to the control subjects (i.e. vehicle group). Interestingly, Vit D treatment supplementation reversed the mentioned effects of UCMS. Our findings indicated that Vit D administration improves UCMS-induced impairment of learning and memory through prevention of adverse effects on Aβ, BDNF and oxidative stress parameters.

The Effects of Early Life Stress on the Brain and Behaviour: Insights From Zebrafish Models

The early life period represents a window of increased vulnerability to stress, during which exposure can lead to long-lasting effects on brain structure and function. This stress-induced developmental programming may contribute to the behavioural changes observed in mental illness. In recent decades, rodent studies have significantly advanced our understanding of how early life stress (ELS) affects brain development and behaviour. These studies reveal that ELS has long-term consequences on the brain such as impairment of adult hippocampal neurogenesis, altering learning and memory. Despite such advances, several key questions remain inadequately answered, including a comprehensive overview of brain regions and molecular pathways that are altered by ELS and how ELS-induced molecular changes ultimately lead to behavioural changes in adulthood. The zebrafish represents a novel ELS model, with the potential to contribute to answering some of these questions. The zebrafish offers some important advantages such as the ability to non-invasively modulate stress hormone levels in a whole animal and to visualise whole brain activity in freely behaving animals. This review discusses the current status of the zebrafish ELS field and its potential as a new ELS model.

Novel rapid-acting glutamatergic modulators: Targeting the synaptic plasticity in depression

Major depressive disorder (MDD) is severely prevalent, and conventional monoaminergic antidepressants gradually exhibit low therapeutic efficiency, especially for patients with treatment-resistant depression. A neuroplasticity hypothesis is an emerging advancement in the mechanism of depression, mainly expressed in the glutamate system, e.g., glutamate receptors and signaling. Dysfunctional glutamatergic neurotransmission is currently considered to be closely associated with the pathophysiology of MDD. Biological function, pharmacological action, and signal attributes in the glutamate system both regulate the neural process. Specific functional subunits could be therapeutic targets to explore the novel glutamatergic modulators, which have fast-acting, and relatively sustained antidepressant effects. Here, the present review summarizes the pathophysiology of MDD found in the glutamate system, exploring the role of glutamate receptors and their downstream effects. These convergent mechanisms have prompted the development of other modulators targeting on glutamate system, including N-methyl-d-aspartate receptor antagonists, selective GluN2B-specific antagonists, glycine binding site agents, and regulators of metabotropic glutamate receptors. Relevant researches underly the putative mechanisms of these drugs, which reverse the damage of depression by regulating glutamatergic neurotransmission. It also provides further insight into the mechanism of depression and exploring potential targets for novel agent development.

Effects of datumetine on hippocampal NMDAR activity

The usage (abuse) of Datura metel is becoming increasingly worrisome among the Nigerian populace especially among the youth considering its side effects such as hallucination. This work was designed to identify the phytochemicals in datura plant that potentially interact with NMDAR as it affects the electrical and memory activities of the brain. Ligand-protein interaction was assessed using autodock vina to identify phytochemicals that can interact with NMDAR. Datumetine was found to have the best interaction fit with NMDAR at both allosteric and orthosteric binding sites. Furthermore, using electrophysiological, behavioural and western blotting techniques, it was observed that the administration of datumetine positively modulates the NMDAR current by prolonging burst duration and interspike interval, induces seizures in C57BL/6 mice. Acute exposure leads to memory deficit on NOR and Y-maze test while immunoblotting results showed increased expression of GluN1 and CamKIIα while pCamKIIα-T286, CREB and BDNF were downregulated. The results showed that the memory deficit seen in datura intoxication is possibly the effects of datumetine on NMDAR.

Early-life stress effects on BDNF DNA methylation in first-episode psychosis and in rats reared in isolation

Stressful events during early-life are risk factors for psychiatric disorders. Brain-derived neurotrophic factor (BDNF) is implicated in psychosis pathophysiology and deficits in BDNF mRNA in animal models of psychiatric disease are reported. DNA methylation can control gene expression and may be influenced by environmental factors such as early-life stress. We investigated BDNF methylation in first-episode psychosis (FEP) patients (n = 58), their unaffected siblings (n = 29) and community-based controls (n = 59), each of whom completed the Childhood Trauma Questionnaire (CTQ); BDNF methylation was also tested in male Wistar rats housed isolated or grouped from weaning. DNA was extracted from human blood and rat brain (prefrontal cortex and hippocampus), bisulphite-converted and the methylation of equivalent sequences within BDNF exon IV determined by pyrosequencing. BDNF methylation did not differ significantly between diagnostic groups; however, individuals who had experienced trauma presented higher levels of methylation. We found association between the mean BDNF methylation and total CTQ score in FEP, as well as between individual CpG sites and subtypes of trauma. No significant correlations were found for controls or siblings with child trauma. These results were independent of age, gender, body mass index, BDNF genotype or LINE-1, a measure of global methylation, which showed no significant association with trauma. Isolation rearing resulted in increased BDNF methylation in both brain regions compared to group-housed animals, a correlate of previously reported changes in gene expression. Our results suggest that childhood maltreatment may result in increased BDNF methylation, providing a mechanism underlying the association between early-life stress and psychosis.

Estrogen administration attenuates post-stroke depression by enhancing CREB/BDNF/TrkB signaling in the rat hippocampus

A previous study demonstrated that 17β-estradiol (E2), which is an antidepressant, can ameliorate post-stroke depression (PSD); however, the underlying mechanisms governing this remain largely unknown. Therefore, the present study developed a PSD model in rats, which was induced by left middle cerebral artery occlusion followed by exposure to chronic mild stress for 2 weeks. The results revealed that the activity of the cAMP response element-binding protein (CREB), a cellular transcription factor, and the associated brain-derived neurotrophic factor (BDNF)/tyrosine kinase B (TrkB) signaling were all attenuated in the hippocampus in PSD rats. The depression-like behaviors were significantly improved after treatment with E2, along with increased CREB and the BDNF/TrkB signaling activity. These results provide novel insight into the molecular basis of PSD, and suggest the potential involvement of CREB/BDNF/TrkB signaling in E2-mediated improvement of PSD in rats.

Robustly High Hippocampal BDNF levels under Acute Stress in Mice Lacking the Full-length p75 Neurotrophin Receptor

BACKGROUND

Brain-derived neurotrophic factor (BDNF) exerts its effects on neural plasticity via 2 distinct receptor types, the tyrosine kinase TrkB and the p75 neurotrophin receptor (p75NTR). The latter can promote inflammation and cell death while TrkB is critically involved in plasticity and memory, particularly in the hippocampus. Acute and chronic stress have been associated with suppression of hippocampal BDNF expression and impaired hippocampal plasticity. We hypothesized that p75NTR might be involved in the hippocampal stress response, in particular in stress-induced BDNF suppression, which might be accompanied by increased neuroinflammation.

METHOD

We assessed hippocampal BDNF protein concentrations in wild-type mice compared that in mice lacking the long form of the p75NTR (p75NTR^ExIII-/-) with or without prior exposure to a 1-hour restraint stress challenge. Hippocampal BDNF concentrations were measured using an optimized ELISA. Furthermore, whole-brain mRNA expression of pro-inflammatory interleukin-6 (Il6) was assessed with RT-PCR.

RESULTS

Deletion of full-length p75NTR was associated with higher hippocampal BDNF protein concentration in the stress condition, suggesting persistently high hippocampal BDNF levels in p75NTR-deficient mice, even under stress. Stress elicited increased whole-brain Il6 mRNA expression irrespective of genotype; however, p75NTR^ExIII-/- mice showed elevated baseline Il6 expression and thus a lower relative increase.

CONCLUSIONS

Our results provide evidence for a role of p75NTR signaling in the regulation of hippocampal BDNF levels, particularly under stress. Furthermore, p75NTR signaling modulates baseline but not stress-related Il6 gene expression in mice. Our findings implicate p75NTR signaling as a potential pathomechanism in BDNF-dependent modulation of risk for neuropsychiatric disorders.

Repeated maternal separation causes transient reduction in BDNF expression in the medial prefrontal cortex during early brain development, affecting inhibitory neuron development

It is widely accepted that maternal separation (MS) induces stress in children and disrupts neural circuit formation during early brain development. Even though such disruption occurs transiently early in life, its influence persists after maturation, and could lead to various neurodevelopmental disorders. Our recent study revealed that repeated MS reduces the number of inhibitory neurons and synapses in the medial prefrontal cortex (mPFC) and causes mPFC-related social deficits after maturation. However, how MS impedes mPFC development during early brain development remains poorly understood. Here, we focused on brain-derived neurotrophic factor (BDNF) involved in the development of inhibitory neurons, and examined time-dependent BDNF expression in the mPFC during the pre-weaning period in male rats exposed to MS. Our results show that MS attenuates BDNF expression only around the end of the first postnatal week. Likewise, mRNA expression of activity-regulated cytoskeleton-associated protein (Arc), an immediate-early gene whose expression is partly regulated by BDNF, also decreased in the MS group along with the reduction in BDNF expression. On the contrary, mRNA expression of tropomyosin-related kinase B (TrkB), which is a BDNF receptor, was scarcely altered, while its protein expression decreased in the MS group only during the weaning period. In addition, MS reduced mRNA levels of glutamic acid decarboxylase (GAD) 65, a GABA synthesizing enzyme, only during the weaning period. Our results suggest that repeated MS temporarily attenuates BDNF signaling in the mPFC during early brain development. BDNF plays a crucial role in the development of inhibitory neurons; therefore, transient attenuation of BDNF signaling may cause delays in GABAergic neuron development in the mPFC.

The Relationships Between Stress, Mental Disorders, and Epigenetic Regulation of BDNF

Brain-derived neurotrophic factor (BDNF), a critical member of the neurotrophic family, plays an important role in multiple stress-related mental disorders. Although alterations in BDNF in multiple brain regions of individuals experiencing stress have been demonstrated in previous studies, it appears that a set of elements are involved in the complex regulation. In this review, we summarize the specific brain regions with altered BDNF expression during stress exposure. How various environmental factors, including both physical and psychological stress, affect the expression of BDNF in specific brain regions are further summarized. Moreover, epigenetic regulation of BDNF, including DNA methylation, histone modification, and noncoding RNA, in response to diverse types of stress, as well as sex differences in the sensitivity of BDNF to the stress response, is also summarized. Clarification of the underlying role of BDNF in the stress process will promote our understanding of the pathology of stress-linked mental disorders and provide a potent target for the future treatment of stress-related illness.

Early life stress delays hippocampal development and diminishes the adult stem cell pool in mice

Early life stress predisposes to mental illness and behavioral dysfunction in adulthood, but the mechanisms underlying these persistent effects are poorly understood. Stress throughout life impairs the structure and function of the hippocampus, a brain system undergoing considerable development in early life. The long-term behavioral consequences of early life stress may therefore be due in part to interference with hippocampal development, in particular with assembly of the dentate gyrus (DG) region of the hippocampus. We investigated how early life stress produces long-term alterations in DG structure by examining DG assembly and the generation of a stable adult stem cell pool in routine housing and after stress induced by the limited bedding/nesting paradigm in mice. We found that early life stress leads to a more immature, proliferative DG than would be expected for the animal's age immediately after stress exposure, suggesting that early life stress delays DG development. Adult animals exposed to early life stress exhibited a reduction in the number of DG stem cells, but unchanged neurogenesis suggesting a depletion of the stem cell pool with compensation in the birth and survival of adult-born neurons. These results suggest a developmental mechanism by which early life stress can induce long-term changes in hippocampal function by interfering with DG assembly and ultimately diminishing the adult stem cell pool.

Glucocorticoid Receptor Stimulation Resulting from Early Life Stress Affects Expression of DNA Methyltransferases in Rat Prefrontal Cortex

Early life stress initiates long-term neurobiological changes that affect stress resilience and increased susceptibility to psychopathology. Maternal separation (MS) is used to cause early life stress and it induces profound neurochemical and behavioral changes that last until adulthood. The molecular pathways of how MS affects the regulation of DNA methyltransferases (Dnmt) in brain have not been entirely characterized. We evaluated MS effects on Dnmt1, Dnmt3a and Dnmt3b expression, DNMT enzyme activity and glucocorticoid receptor (GR) recruitment to different Dnmt loci in the prefrontal cortex (PFC) of Wistar rats. We found increased plasma corticosterone levels after MS that were associated with induced Dnmt expression and enzyme activity in rat PFC at post-natal day 15 (PND15). Chromatin immunoprecipitation showed increased binding of GR at the Dnmt3b promoter after MS, suggesting that genomic signaling of GR is an important regulatory mechanism for the induced Dnmt3b expression and DNMT activity. Although GR also binds to Dnmt3a promoter and a putative regulatory region in intron 3 in rat PFC, its expression after maternal separation may be influenced by other mechanisms. Therefore, GR could be a link between early life stress experience and long-term gene expression changes induced by aberrant DNA methylation.

Modulation of neuroplasticity-related targets following stress-induced acute escape deficit

Understanding resilience is a major challenge to improve current pharmacological therapies aimed at complementing psychological-based approaches of stress-related disorders. In particular, resilience is a multi-factorial construct where the complex network of molecular events that drive the process still needs to be resolved. Here, we exploit the acute escape deficit model, an animal model based on exposure to acute unavoidable stress followed by an escape test, to define vulnerable and resilient phenotypes in rats. Hippocampus and prefrontal cortex (PFC), two of the brain areas most involved in the stress response, were analysed for gene expression at two different time points (3 and 24 h) after the escape test. Total Brain-Derived Neurotrophic Factor (BDNF) was highly responsive in the PFC at 24-h after the escape test, while expression of BDNF transcript IV increased in the hippocampus of resistant animals 3 h post-test. Expression of memory enhancers like Neuronal PAS Domain Protein 4 (Npas4) and Activity-regulated cytoskeleton-associated protein (Arc) decreased in a time- and region-dependent fashion in both behavioural phenotypes. Also, the memory inhibitor Protein Phosphatase 1 (Ppp1ca) was increased in the hippocampus of resilient rats at 3 h post-test. Given the importance of neurotrophic factors and synaptic plasticity-related genes for the development of appropriate coping strategies, our data contribute to an additional step forward in the comprehension of the psychobiology of stress and resiliency.

Social Environment and Epigenetics

Our social environment, from the microscopic to the macro-social, affects us for the entirety of our lives. One integral line of research to examine how interpersonal and societal environments can get "under the skin" is through the lens of epigenetics. Epigenetic mechanisms are adaptations made to our genome in response to our environment which include tags placed on and removed from the DNA itself to how our DNA is packaged, affecting how our genes are read, transcribed, and interact. These tags are affected by social environments and can persist over time; this may aid us in responding to experiences and exposures, both the enriched and the disadvantageous. From memory formation to immune function, the experience-dependent plasticity of epigenetic modifications to micro- and macro-social environments may contribute to the process of learning from comfort, pain, and stress to better survive in whatever circumstances life has in store.

Changes in neuroplasticity following early-life social adversities: the possible role of brain-derived neurotrophic factor

Social adversities experienced in childhood can have a profound impact on the developing brain, leading to the emergence of psychopathologies in adulthood. Despite the burden this places on both the individual and society, the neurobiological aspects mediating this transition remain unclear. Recent advances in preclinical and clinical research have begun examining neuroplasticity-the nervous system's ability to form adaptive changes in response to new experience-in the context of early-life vulnerability to social adversities and plasticity-related alterations following such traumatic events. A key mediator of plasticity-related molecular processes is the brain-derived neurotrophic factor (BDNF), which has also been implicated in various psychiatric disorders related to childhood social adversities. Preclinical and clinical data suggest early-life social adversities (ELSA) might be associated with accelerated maturation of social network circuitry, a possible ontogenic adaptation to the adverse environment. Neural plasticity decreases by adulthood, lessening the efficacy of treatment in ELSA-related psychiatric disorders. However, literature data suggest that by increasing BDNF/TrkB signalling through antidepressant treatment a juvenile-like plasticity state can be induced, which allows for reorganization of the social circuitry when guided by psychotherapy and surrounded by a safe and positive environment.

Effect of Acute Stress on the Expression of BDNF, trkB, and PSA-NCAM in the Hippocampus of the Roman Rats: A Genetic Model of Vulnerability/Resistance to Stress-Induced Depression

The Roman High-Avoidance (RHA) and the Roman Low-Avoidance (RLA) rats, represent two psychogenetically-selected lines that are, respectively, resistant and prone to displaying depression-like behavior, induced by stressors. In the view of the key role played by the neurotrophic factors and neuronal plasticity, in the pathophysiology of depression, we aimed at assessing the effects of acute stress, i.e., forced swimming (FS), on the expression of brain-derived neurotrophic factor (BDNF), its trkB receptor, and the Polysialilated-Neural Cell Adhesion Molecule (PSA-NCAM), in the dorsal (dHC) and ventral (vHC) hippocampus of the RHA and the RLA rats, by means of western blot and immunohistochemical assays. A 15 min session of FS elicited different changes in the expression of BDNF in the dHC and the vHC. In RLA rats, an increment in the CA2 and CA3 subfields of the dHC, and a decrease in the CA1 and CA3 subfields and the dentate gyrus (DG) of the vHC, was observed. On the other hand, in the RHA rats, no significant changes in the BDNF levels was seen in the dHC and there was a decrease in the CA1, CA3, and DG of the vHC. Line-related changes were also observed in the expression of trkB and PSA-NCAM. The results are consistent with the hypothesis that the differences in the BDNF/trkB signaling and neuroplastic mechanisms are involved in the susceptibility of RLA rats and resistance of RHA rats to stress-induced depression.

Beyond good and evil: A putative continuum-sorting hypothesis for the functional role of proBDNF/BDNF-propeptide/mBDNF in antidepressant treatment

Depression and posttraumatic stress disorder are assumed to be maladaptive responses to stress and antidepressants are thought to counteract such responses by increasing BDNF (brain-derived neurotrophic factor) levels. BDNF acts through TrkB (tropomyosin-related receptor kinase B) and plays a central role in neuroplasticity. In contrast, both precursor proBDNF and BDNF propeptide (another metabolic product from proBDNF cleavage) have a high affinity to p75 receptor (p75R) and usually convey apoptosis and neuronal shrinkage. Although BDNF and proBDNF/propeptide apparently act in opposite ways, neuronal turnover and remodeling might be a final common way that both act to promote more effective neuronal networking, avoiding neuronal redundancy and the misleading effects of environmental contingencies. This review aims to provide a brief overview about the BDNF functional role in antidepressant action and about p75R and TrkB signaling to introduce the "continuum-sorting hypothesis." The resulting hypothesis suggests that both BDNF/proBDNF and BDNF/propeptide act as protagonists to fine-tune antidepressant-dependent neuroplasticity in crucial brain structures to modulate behavioral responses to stress.

The dose makes the poison: from glutamate-mediated neurogenesis to neuronal atrophy and depression

Experimental evidence has demonstrated that glutamate is an essential factor for neurogenesis, whereas another line of research postulates that excessive glutamatergic neurotransmission is associated with the pathogenesis of depression. The present review shows that such paradox can be explained within the framework of hormesis, defined as biphasic dose responses. Low glutamate levels activate adaptive stress responses that include proteins that protect neurons against more severe stress. Conversely, abnormally high levels of glutamate, resulting from increased release and/or decreased removal, cause neuronal atrophy and depression. The dysregulation of the glutamatergic transmission in depression could be underlined by several factors including a decreased inhibition (γ-aminobutyric acid or serotonin) or an increased excitation (primarily within the glutamatergic system). Experimental evidence shows that the activation of N-methyl-D-aspartate receptor (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPAR) can exert two opposite effects on neurogenesis and neuron survival depending on the synaptic or extrasynaptic concentration. Chronic stress, which usually underlies experimental and clinical depression, enhances glutamate release. This overactivates NMDA receptors (NMDAR) and consequently impairs AMPAR activity. Various studies show that treatment with antidepressants decreases plasma glutamate levels in depressed individuals and regulates glutamate receptors by reducing NMDAR function by decreasing the expression of its subunits and by potentiating AMPAR-mediated transmission. Additionally, it has been shown that chronic treatment with antidepressants having divergent mechanisms of action (including tricyclics, selective serotonin reuptake inhibitors, and ketamine) markedly reduced depolarization-evoked glutamate release in the hippocampus. These data, taken together, suggest that the glutamatergic system could be a final common pathway for antidepressant treatments.

Hippocampal BDNF in physiological conditions and social isolation

Exposure of an organism to chronic psychosocial stress may affect brain-derived neurotrophic factor (BDNF) expression that has been implicated in the etiology of psychiatric disorders, such as depression. Given that depression in humans has been linked with social stress, the chronic social stress paradigms for modeling psychiatric disorders in animals have thus been developed. Chronic social isolation in animal models generally causes changes in hypothalamic-pituitary-adrenal axis functioning, associated with anxiety- and depressive-like behaviors. Also, this chronic stress causes downregulation of BDNF protein and mRNA in the hippocampus, a stress-sensitive brain region closely related to the pathophysiology of depression. In this review, we discuss the current knowledge regarding the structure, function, intracellular signaling, inter-individual differences and epigenetic regulation of BDNF in both physiological conditions and depression and changes in corticosterone levels, as a marker of stress response. Since BDNF levels are age dependent in humans and rodents, this review will also highlight the effects of adolescent and adult chronic social isolation models of both genders on the BDNF expression.

Glucocorticoid receptor represses brain-derived neurotrophic factor expression in neuron-like cells

Brain-derived neurotrophic factor (BDNF) is involved in many functions such as neuronal growth, survival, synaptic plasticity and memorization. Altered expression levels are associated with many pathological situations such as depression, epilepsy, Alzheimer’s, Huntington’s and Parkinson’s diseases. Glucocorticoid receptor (GR) is also crucial for neuron functions, via binding of glucocorticoid hormones (GCs). GR actions largely overlap those of BDNF. It has been proposed that GR could be a regulator of BDNF expression, however the molecular mechanisms involved have not been clearly defined yet. Herein, we analyzed the effect of a GC agonist dexamethasone (DEX) on BDNF expression in mouse neuronal primary cultures and in the newly characterized, mouse hippocampal BZ cell line established by targeted oncogenesis. Mouse Bdnf gene exhibits a complex genomic structure with 8 untranslated exons (I to VIII) splicing onto one common and unique coding exon IX. We found that DEX significantly downregulated total BDNF mRNA expression by around 30%. Expression of the highly expressed exon IV and VI containing transcripts was also reduced by DEX. The GR antagonist RU486 abolished this effect, which is consistent with specific GR-mediated action. Transient transfection assays allowed us to define a short 275 bp region within exon IV promoter responsible for GR-mediated Bdnf repression. Chromatin immunoprecipitation experiments demonstrated GR recruitment onto this fragment, through unidentified transcription factor tethering. Altogether, GR downregulates Bdnf expression through direct binding to Bdnf regulatory sequences. These findings bring new insights into the crosstalk between GR and BDNF signaling pathways both playing a major role in physiology and pathology of the central nervous system.

Neonatal Proinflammatory Stress Induces Accumulation of Corticosterone and Interleukin-6 in the Hippocampus of Juvenile Rats: Potential Mechanism of Synaptic Plasticity Impairments

Infectious diseases in early postnatal ontogenesis can induce neuroinflammation, disrupt normal central nervous system development, and contribute to pathogenesis of cerebral pathologies in adults. To study long-term consequences of such early stress, we induced neonatal proinflammatory stress (NPS) by injecting bacterial lipopolysaccharide into rat pups on postnatal days 3 and 5 and then assessed the levels of corticosterone, proinflammatory cytokines and their mRNAs, and neurotrophins and their mRNAs in the hippocampus and neocortex of the one-month-old animals. Long-term potentiation (LTP) was studied in hippocampal slices as an index of synaptic plasticity. NPS-induced impairments of LTP were accompanied by the accumulation of corticosterone and IL-6 in the hippocampus. In the neocortex, a decrease in exon IV BDNF mRNA was detected. We suggest that excessive corticosterone delivery to hippocampal receptors and proinflammatory changes persisting during brain maturation are among the principal molecular mechanisms responsible for NPS-induced neuroplasticity impairments.

Brain-derived neurotrophic factor and early-life stress: Multifaceted interplay

The brain-derived neurotrophic factor (BDNF) is a key regulator of neural development and plasticity. Longterm changes in the BDNF pathway are associated with childhood adversity and adult depression symptoms. Initially, stress-induced decreases in the BDNF pathway were found in some studies, but subsequent reports indicated the relationship between stress and BDNF to be much more complex, and the concept was significantly revised. In the present mini-review, we focus on the structure and regulation of the Bbnf gene as well as on the stress-BDNF interactions under early-life adverse conditions.

Prolonged maternal separation attenuates BDNF-ERK signaling correlated with spine formation in the hippocampus during early brain development

Maternal separation (MS) is known to affect hippocampal function such as learning and memory, yet the molecular mechanism remains unknown. We hypothesized that these impairments are attributed to abnormities of neural circuit formation by MS, and focused on brain-derived neurotrophic factor (BDNF) as key factor because BDNF signaling has an essential role in synapse formation during early brain development. Using rat offspring exposed to MS for 6 h/day during postnatal days (PD) 2-20, we estimated BDNF signaling in the hippocampus during brain development. Our results show that MS attenuated BDNF expression and activation of extracellular signal-regulated kinase (ERK) around PD 7. Moreover, plasticity-related immediate early genes, which are transcriptionally regulated by BDNF-ERK signaling, were also reduced by MS around PD 7. Interestingly, detailed analysis revealed that MS particularly reduced expression of BDNF gene and immediate early genes in the cornu ammonis 1 (CA1) of hippocampus at PD 7. Considering that BDNF-ERK signaling is involved in spine formation, we next evaluated spine formation in the hippocampus during the weaning period. Our results show that MS particularly reduced mature spine density in proximal apical dendrites of CA1 pyramidal neurons at PD 21. These results suggest that MS could attenuate BDNF-ERK signaling during primary synaptogenesis with a region-specific manner, which is likely to lead to decreased spine formation and maturation observed in the hippocampal CA1 region. It is speculated that this incomplete spine formation during early brain development has an influence on learning capabilities throughout adulthood.

Stress-induced change in serum BDNF is related to quantitative family history of alcohol use disorder and age at first alcohol use

Previous research in animal models suggests that brain-derived neurotrophic factor (BDNF) is involved in stress-modulated alcohol consumption. However, relatively few studies have investigated this issue in humans, and results of existing studies have been heterogeneous. The primary aim of the current study was to examine the within-subjects effect of acute stress (timed math plus cold pressor) on serum BDNF levels (ΔBDNF: post- minus pre-stress) in healthy social drinkers (N=68, 20 male). A secondary aim was to explore which heritable and environmental factors in our limited sample might exert the greatest influences on ΔBDNF. Importantly, presence versus absence of the BDNF Val⁶⁶Met polymorphism (rs6265), which has often been discounted in studies of human serum BDNF, was included as a between-subjects control variable in all statistical analyses. Our results indicated that acute stress decreased serum BDNF. Further, multiple regression analyses revealed that quantitative family history of alcohol use disorder (qFH) and age at first alcohol use together accounted for 15% of the variance in ΔBDNF. Thus, the influences of qFH and age at first alcohol use may explain some of the heterogeneity that exists in previous studies of human serum BDNF. These results parallel findings in animal models and suggest that stress-related changes in serum BDNF are influenced by both heritable (qFH) and environmental (early alcohol consumption) factors.

Running during adolescence rescues a maternal separation-induced memory impairment in female mice: Potential role of differential exon-specific BDNF expression

Exposure to early life stress has been associated with memory impairments related to changes in brain-derived neurotrophic factor (BDNF) signaling. However, the potential impact of physical exercise to reverse these effects of maternal separation has been under investigated. Mice were subjected to maternal separation during the first 2 weeks of life and then exposed to a 3-week running protocol during adolescence. The spontaneous object recognition task was performed during adolescence followed by analysis of hippocampal expression of exons I, IV, and IX of the BDNF gene. As expected, maternal separation impaired recognition memory and this effect was reversed by exercise. In addition, running increased BDNF exon I expression, but decreased expression of BDNF exon IV in all groups, while exon IX expression increased only in MS animals exposed to exercise. Our data suggest that memory deficits can be attenuated by exercise and specific transcripts of the BDNF gene are dynamically regulated following both MS and exercise.

Functional Role of BDNF Production from Unique Promoters in Aggression and Serotonin Signaling

Brain-derived neurotrophic factor (BDNF) regulates diverse biological functions ranging from neuronal survival and differentiation during development to synaptic plasticity and cognitive behavior in the adult. BDNF disruption in both rodents and humans is associated with neurobehavioral alterations and psychiatric disorders. A unique feature of Bdnf transcription is regulation by nine individual promoters, which drive expression of variants that encode an identical protein. It is hypothesized that this unique genomic structure may provide flexibility that allows different factors to regulate BDNF signaling in distinct cell types and circuits. This has led to the suggestion that isoforms may regulate specific BDNF-dependent functions; however, little scientific support for this idea exists. We generated four novel mutant mouse lines in which BDNF production from one of the four major promoters (I, II, IV, or VI) is selectively disrupted (Bdnf-e1, -e2, -e4, and -e6 mice) and used a comprehensive comparator approach to determine whether different Bdnf transcripts are associated with specific BDNF-dependent molecular, cellular, and behavioral phenotypes. Bdnf-e1 and -e2 mutant males displayed heightened aggression accompanied by convergent expression changes in specific genes associated with serotonin signaling. In contrast, BDNF-e4 and -e6 mutants were not aggressive but displayed impairments associated with GABAergic gene expression. Moreover, quantifications of BDNF protein in the hypothalamus, prefrontal cortex, and hippocampus revealed that individual Bdnf transcripts make differential, region-specific contributions to total BDNF levels. The results highlight the biological significance of alternative Bdnf transcripts and provide evidence that individual isoforms serve distinct molecular and behavioral functions.

The HDAC inhibitor SAHA improves depressive-like behavior of CRTC1-deficient mice: Possible relevance for treatment-resistant depression

Major depression is a highly complex disabling psychiatric disorder affecting millions of people worldwide. Despite the availability of several classes of antidepressants, a substantial percentage of patients are unresponsive to these medications. A better understanding of the neurobiology of depression and the mechanisms underlying antidepressant response is thus critically needed. We previously reported that mice lacking CREB-regulated transcription coactivator 1 (CRTC1) exhibit a depressive-like phenotype and a blunted antidepressant response to the selective serotonin reuptake inhibitor fluoxetine. In this study, we similarly show that Crtc1(-/-) mice are resistant to the antidepressant effect of chronic desipramine in a behavioral despair paradigm. Supporting the blunted response to this tricyclic antidepressant, we found that desipramine does not significantly increase the expression of Bdnf and Nr4a1-3 in the hippocampus and prefrontal cortex of Crtc1(-/-) mice. Epigenetic regulation of neuroplasticity gene expression has been associated with depression and antidepressant response, and histone deacetylase (HDAC) inhibitors have been shown to have antidepressant-like properties. Here, we show that unlike conventional antidepressants, chronic systemic administration of the HDAC inhibitor SAHA partially rescues the depressive-like behavior of Crtc1(-/-) mice. This behavioral effect is accompanied by an increased expression of Bdnf, but not Nr4a1-3, in the prefrontal cortex of these mice, suggesting that this epigenetic intervention restores the expression of a subset of genes by acting downstream of CRTC1. These findings suggest that CRTC1 alterations may be associated with treatment-resistant depression, and support the interesting possibility that targeting HDACs may be a useful therapeutic strategy in antidepressant development.

Gestational stress induces depressive-like and anxiety-like phenotypes through epigenetic regulation of BDNF expression in offspring hippocampus

Exposure to stressful life events during pregnancy exerts profound effects on neurodevelopment and increases the risk for several neurodevelopmental disorders including major depression. The mechanisms underlying the consequences of gestational stress are complex and remain to be elucidated. This study investigated the effects of gestational stress on depressive-like behavior and epigenetic modifications in young adult offspring. Gestational stress was induced by a combination of restraint and 24-hour light disturbance to pregnant dams throughout gestation. Depressive-like and anxiety-like behaviors of young adult offspring were examined. The expression and promoter methylation of brain derived neurotrophic factor (BDNF) were measured using RT-qPCR, Western blot, methylated DNA immunoprecipitation (MeDIP) and chromatin immunoprecipitation (ChIP). In addition, the expressions of histone deacetylases (HDACs) and acetylated histone H3 lysine 14 (AcH3K14) were also analyzed. Our results show that offspring from gestational stress dams exhibited depressive-like and anxiety-like behaviors. Biochemically, stress-offspring showed decreased expression of BDNF, increased expression of DNMT1, HDAC1, and HDAC2, and decreased expression of AcH3K14 in the hippocampus as compared to non-stress offspring. Data from MeDIP and ChIP assays revealed an increased methylation as well as decreased binding of AcH3K14 on specific BDNF promoters. Pearson analyses indicated that epigenetic changes induced by gestational stress were correlated with depressive-like and anxiety-like behaviors. These data suggest that gestational stress may be a suitable model for understanding the behavioral and molecular epigenetic changes observed in patients with depression.

Impact of exercise and vitamin B1 intake on hippocampal brain-derived neurotrophic factor and spatial memory performance in a rat model of stress

Chronic stress affects brain areas involved in learning and emotional responses through modulation of neurotropic factors or neurotransmitters. Therefore, we investigated the role of exercise and thiamine supplementation on spatial memory and on brain-derived neurotrophic factor (BDNF) and acetylcholine (Ach) content in the hippocampus of the stressed animals. Male Wistar rats were randomly assigned to 4 groups (8 rats/group): control group; stress group; swimming and stress group; and thiamine and stress group. All animals were assessed by a T maze for spatial memory or open field test for locomotion and anxiety. BDNF and Ach were estimated in the hippocampus. Chronic immobilization stress resulted in a significant decrease in BDNF and Ach levels in the hippocampus and impairment in spatial memory functions and decreased basal activity. However, either swimming training or thiamine intake for 30 d was proved to induce a significant increase both in BDNF and Ach in conjunction with improved performance in the T maze, marked anxiolytic effect and enhanced ambulation in the open field test, as compared to the stress group. Interestingly, swimming-exercised rats showed significantly higher levels of BDNF versus thiamine-receiving rats, while thiamine-receiving rats showed higher locomotor activity and less freezing behavior in the open field test compared to the swimming group. It was concluded that decreased BDNF and Ach after stress exposure could be a mechanism for the deleterious actions of stress on memory function; swimming exercise or vitamin B1 supplementation for 30 d was a protective tool to improve coping with chronic stress by modulating BDNF and Ach content along with enhancement of memory functions and motor activities.

Emerging treatment mechanisms for depression: focus on glutamate and synaptic plasticity

Major depression is a chronic and debilitating illness that effects approximately 1 in 5 people, but currently available treatments are limited by low rates of efficacy, therapeutic time lag, and undesirable side effects. Recent efforts have been directed towards investigating rapid-acting agents that reverse the behavioral and neuronal deficits of chronic stress and depression, notably the glutamate NMDA receptor antagonist ketamine. The cellular mechanisms underlying the rapid antidepressant actions of ketamine and related agents are discussed, as well as novel, selective glutamatergic receptor targets that are safer and have fewer side effects.

The Impact of Parent-Infant Interaction on Epigenetic Plasticity Mediating Synaptic Adaptations in the Infant Brain

The development of the brain depends on an individual's nature (genes) and nurture (environments). This interaction between genetic predispositions and environmental events during brain development drives the maturation of functional brain circuits such as sensory, motor, emotional, and complex cognitive pathways. Adverse environmental conditions such as early life stress can interfere with the functional development of emotional and cognitive brain systems and thereby increase the risk of developing psychiatric disorders later in life. In order to develop more efficient and individualized protective and therapeutic interventions, it is essential to understand how environmental stressors during infancy affect cellular and molecular mechanisms involved in brain maturation. Animal models of early life stress have been able to reveal brain structural and metabolic changes in prefrontolimbic circuits, which are time, brain region, neuron, and sex specific. By focusing on animal models of separation stress during infancy, this review highlights epigenetic and cytoarchitectural modifications which are assumed to mediate lasting changes of brain function and behavior.

Blunted behavioral and molecular responses to chronic mild stress in adult rats with experience of infancy maternal separation

Childhood adversity has profound and persistent effects on brain functions and has been implicated in the etiology of depression. Brain-derived neurotrophic factor (BDNF) and cAMP response element-binding protein (CREB) play critical roles during brain development to maintain neuronal function and structural integrity in adulthood. We therefore investigated the long-term effects of early life adversity on the depression-related behavior and the expression of BDNF and CREB in the hippocampus. Male Sprague-Dawley newborn rats were subjected to maternal separation for 3 h/day on postnatal days 2-14. After the postnatal day 90, rats with or without the experience of infancy maternal separation received a series of unpredictable chronic mild stress (CMS) for 21 days. Sucrose preference and spontaneous activity in the open field test were recorded, and the expression of BDNF and CREB in the hippocampus was measured by real-time RT-PCR and Western blot analyses. Before exposure to CMS, the rats with maternal separation showed the significant decreases in sucrose preference, spontaneous activity, and hippocampal expression of BDNF and CREB, compared to the animals without maternal separation. In contrast, the rats without maternal separation showed greater decreases of the above indictors after CMS, the levels of which were lower than those observed in the rats with maternal separation. Thus, early life adversity leads to long-term decreases in the capacity of enjoying sweetness, spontaneous activity, and hippocampal expression of BDNF and CREB. Moreover, childhood neglect may decrease the neurobehavioral plasticity, thereby blunting the responses to adulthood stress and increasing the susceptibility to depression.

Early Life Stress Effects on Glucocorticoid-BDNF Interplay in the Hippocampus

Early life stress (ELS) is implicated in the etiology of multiple psychiatric disorders. Important biological effects of ELS are manifested in stress-susceptible regions of the hippocampus and are partially mediated by long-term effects on glucocorticoid (GC) and/or neurotrophin signaling pathways. GC-signaling mediates the regulation of stress response to maintain homeostasis, while neurotrophin signaling plays a key role in neuronal outgrowth and is crucial for axonal guidance and synaptic integrity. The neurotrophin and GC-signaling pathways co-exist throughout the central nervous system (CNS), particularly in the hippocampus, which has high expression levels of glucocorticoid-receptors (GR) and mineralocorticoid-receptors (MR) as well as brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin-related kinase receptor B (TrkB). This review addresses the effects of ELS paradigms on GC- and BDNF-dependent mechanisms and their crosstalk in the hippocampus, including potential implications for the pathogenesis of common stress-related disorders.

Regulation of Adult Neurogenesis and Plasticity by (Early) Stress, Glucocorticoids, and Inflammation

Exposure to stress is one of the best-known negative regulators of adult neurogenesis (AN). We discuss changes in neurogenesis in relation to exposure to stress, glucocorticoid hormones, and inflammation, with a particular focus on early development and on lasting effects of stress. Although the effects of acute and mild stress on AN are generally brief and can be quickly overcome, chronic exposure or more severe forms of stress can induce longer lasting reductions in neurogenesis that can, however, in part, be overcome by subsequent exposure to exercise, drugs targeting the stress system, and some antidepressants. Exposure to stress, particularly during the sensitive period of early life, may (re)program brain plasticity, in particular, in the hippocampus. This may increase the risk to develop cognitive or anxiety symptoms, common to brain diseases like dementia and depression in which plasticity changes occur, and a normalization of neurogenesis may be required for a successful treatment response and recovery.

Maternal separation produces alterations of forebrain brain-derived neurotrophic factor expression in differently aged rats

Early life adversity, such as postnatal maternal separation (MS), play a central role in the development of psychopathologies during individual ontogeny. In this study, we investigated the effects of repeated MS (4 h per day from postnatal day (PND) 1-21) on the brain-derived neurotrophic factor (BDNF) expression in the medial prefrontal cortex (mPFC), the nucleus accumbens (NAc) and the hippocampus of male and female juvenile (PND 21), adolescent (PND 35) and young adult (PND 56) Wistar rats. The results indicated that MS increased BDNF in the CA1 and the dentate gyrus (DG) of adolescent rats as well as in the DG of young adult rats. However, the expression of BDNF in the mPFC in the young adult rats was decreased by MS. Additionally, in the hippocampus, there was decreased BDNF expression with age in both the MS and non separated rats. However, in the mPFC, the BDNF expression was increased with age in the non separated rats; nevertheless, the BDNF expression was significantly decreased in the MS young adult rats. In the NAc, the BDNF expression was increased with age in the male non-maternal separation (NMS) rats, and the young adult female MS rats had less BDNF expression than the adolescent female MS rats. The present study shows unique age-differently changes on a molecular level induced by MS and advances the use of MS as a valid animal model to detect the underlying neurobiological mechanisms of mental disorders.

Protective effect of young green barley leaf (Hordeum vulgare L.) on restraint stress-induced decrease in hippocampal brain-derived neurotrophic factor in mice

Background:

Many health experts support the hypothesis that stressful lifestyles are the leading cause of illness, like depression. Therefore, from the standpoint of preventive medicine, it is important to reduce stress. Young green barley leaves are a good natural source of vitamins and minerals, and their juice is widely consumed as a functional food for health reasons in Japan. This study investigated the protective effect of young green barley leaves for stress control.

Materials and Methods:

ICR outbred mice were exposed to 3-h sessions of restraint stress. Young green barley leaves (400 and 1,000 mg/kg) were administered orally 1 h before the sessions for 5 days. To analyze voluntary behavior, wheel-running activity was monitored during the dark period. Brain-derived neurotrophic factor (BDNF) messenger RNA (mRNA) expression in the whole hippocampus was measured by real-time quantitative polymerase chain reaction.

Results:

Restraint stress resulted in a significant decrease in voluntary wheel-running behavior, but this decrease was ameliorated by the administration of young green barley leaves. The leaves also enhanced the decreased levels of BDNF mRNA induced by restraint stress; in particular, a significant protective effect was shown in the exon IV variant as compared to vehicle control mice.

Conclusion:

The findings suggest that young green barley leaves have potent anti-stress properties, as evidenced by preventing decreases in the levels of voluntary wheel-running activity and hippocampal BDNF mRNA in response to restraint stress. Our findings support the possibility that supplementation with young green barley leaves might be beneficial for preventing stress-related psychiatric disorders like depression.

Effects of developmental alcohol exposure vs. intubation stress on BDNF and TrkB expression in the hippocampus and frontal cortex of neonatal rats

Third trimester-equivalent alcohol exposure causes significant deficits in hippocampal and cortical neuroplasticity, resulting in alterations to dendritic arborization, hippocampal adult neurogenesis, and performance on learning tasks. The current study investigated the impact of neonatal alcohol exposure (postnatal days 4-9, 5.25 g/kg/day) on expression of brain-derived neurotrophic factor (BDNF) and the tropomyosin-related kinase B (TrkB) receptor in the hippocampal and frontal cortex of infant Long-Evans rats. Levels of BDNF protein were increased in the hippocampus, but not frontal cortex, of alcohol-exposed rats 24h after the last dose, when compared with undisturbed (but not sham-intubated) control animals. BDNF protein levels showed a trend toward increase in hippocampus of sham-intubated animals as well, suggesting an effect of the intubation procedure. TrkB protein was increased in the hippocampus of alcohol-exposed animals compared to sham-intubated pups, indicating an alcohol-specific effect on receptor expression. In addition, expression of bdnf total mRNA in alcohol-exposed and sham-intubated pups was enhanced in the hippocampus; however, there was a differential effect of alcohol and intubation stress on exon I- and IV-specific mRNA transcripts. Further, plasma corticosterone was found to be increased in both alcohol-exposed and sham-intubated pups compared to undisturbed animals. Upregulation of BDNF could potentially represent a neuroprotective mechanism activated following alcohol exposure or stress. The results suggest that alcohol exposure and stress have both overlapping and unique effects on BDNF, and highlight the need for the stress of intubation to be taken into consideration in studies that implement this route of drug delivery.

Gender and brain regions specific differences in brain derived neurotrophic factor protein levels of depressed individuals who died through suicide

Considerable evidence supports the view that depressive illness and suicidal behaviour stem from perturbations of neuroplasticity. Presently, we assessed whether depressed individuals who died by suicide displayed brain region-specific changes in brain derived neurotrophic factor (BDNF) and whether such effects varied by gender. Using postmortem samples from non-psychiatric controls and depressed individuals who died by suicide, BDNF protein levels were assessed within the hippocampus and frontopolar prefrontal cortex using Western blot. As expected, BDNF levels were reduced within the frontopolar prefrontal cortex among female depressed suicides; however, males showed no such effect. Contrastingly, within the hippocampus, depressed male but not female suicides displayed significant reductions of BDNF protein levels. Although the mechanisms driving the gender and brain region specific BDNF changes are unclear, our data do support the notion that complex alterations of neuroplasticity may be fundamentally involved in the illness.